This invention generally relates to a fluid control valve and, more particularly, to a fluid control valve for selectively controlling the flow of a hydraulic fluid at two different pressures to fluid motors. Further yet, this invention relates to a fluid control valve for selectively energizing and deenergizing power assist hydraulic motors coupled to wheels while the high pressure primary hydraulic supply pump is running and, further, while the wheels are rotating.
Vehicles, such as combines, construction fork trucks, road pavers, and vibratory drum rollers are many times driven with a main power source such as from a primary pump coupled to a combustion engine or directly with the combustion engine and by driving the front wheels of the vehicle. Further, the steerable wheels are also often equipped with hydraulic powered motors so as to assist in driving the vehicle. In this fashion, a four-wheel drive vehicle is provided for better performing in rough and slippery terrain such as muddy fields and construction sites.
However, when driving the vehicle i.e., "roading" from field to field or from construction site to construction site, it is most advantageous to disengage the rear wheel hydraulic motors as they are basically not needed and, in fact, unnecessarily heat up and decrease the overall efficiency of the vehicle. Furthermore, such driving of the hydraulic assist motors tend to cause them to fail prematurely. In the past, the rear wheel hydraulic motors have been disengaged from the hydraulic system by first stopping the vehicle, shutting down the combustion engine driving the primary pump or disengaging the primary pump itself and, thereafter, getting out of the vehicle and manually disengaging the hydraulic motors. As can be appreciated, this method of engaging and disengaging the rear wheel assist motors is cumbersome, time-consuming, and also potentially dangerous depending on where the operator must reach so as to disengage the motors.